I hadn't noticed this before, the error message tells as where the rogue data is...
Msg 1505, Level 16, State 1, Line 3
The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.TrackingData' and the index name 'UniqueTrigger'. The duplicate key value is (2008-06-09 07:05:19, 350824225).
Msg 1750, Level 16, State 0, Line 3
Could not create constraint. See previous errors.
The statement has been terminated.